net: rfs: fix crash in get_rps_cpus()

Commit 567e4b79731c ("net: rfs: add hash collision detection") had one
mistake :

RPS_NO_CPU is no longer the marker for invalid cpu in set_rps_cpu()
and get_rps_cpu(), as @next_cpu was the result of an AND with
rps_cpu_mask

This bug showed up on a host with 72 cpus :
next_cpu was 0x7f, and the code was trying to access percpu data of an
non existent cpu.

In a follow up patch, we might get rid of compares against nr_cpu_ids,
if we init the tables with 0. This is silly to test for a very unlikely
condition that exists only shortly after table initialization, as
we got rid of rps_reset_sock_flow() and similar functions that were
writing this RPS_NO_CPU magic value at flow dismantle : When table is
old enough, it never contains this value anymore.

Fixes: 567e4b79731c ("net: rfs: add hash collision detection")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/Documentation/networking/scaling.txt b/Documentation/networking/scaling.txt
index cbfac0949635..59f4db2a0c85 100644
--- a/Documentation/networking/scaling.txt
+++ b/Documentation/networking/scaling.txt
@@ -282,7 +282,7 @@ following is true:
 
 - The current CPU's queue head counter >= the recorded tail counter
   value in rps_dev_flow[i]
-- The current CPU is unset (equal to RPS_NO_CPU)
+- The current CPU is unset (>= nr_cpu_ids)
 - The current CPU is offline
 
 After this check, the packet is sent to the (possibly updated) current